In situmonitoring the productivity of ultra-small gold nanoparticles generated by pulsed-laser ablation of a high-speed rotating gold target in pure water

We investigate the productivity of ultra-small gold nanoparticles generated by pulsed-laser ablation in liquid of a high-speed rotating gold target as functions of laser ablation time and rotation speed of the target in the range 90-3000 rpm. These experiments were performed byin situmonitoring the extinction spectra of the gold colloidal suspension. The time evolution of the gold volume fraction in the colloidal suspension of the target was determined by modeling the extinction spectra using the shape distribution effective medium theory. The time dependence of the ablation rate, deduced from that of the volume fraction, shows an initial exponential decay followed by a steady-state value at longer ablation time. The influence of the laser-induced roughening of the target surface on the time evolution of the ablation rate is clearly demonstrated. The experimental results also reveal the dependence of the time evolution of the ablation rate of the target on its rotation speed. The effect of the liquid flow on the ablation rate of the target is analyzed and discussed.

Silver Nanoparticles Produced by Laser Ablation and Re-Irradiation Are Effective Preventing Peri-Implantitis Multispecies Biofilm Formation

Implant-associated infection due to biofilm formation is a growing problem. Given that silver nanoparticles (Ag-NPs) have shown antibacterial effects, our goal is to study their effect against multispecies biofilm involved in the development of peri-implantitis. To this purpose, Ag-NPs were synthesized by laser ablation in de-ionized water using two different lasers, leading to the production of colloidal suspensions. Subsequently, part of each suspension was subjected to irradiation one and three times with the same laser source with which it was obtained. Ag-NPs were immobilized on the surface of titanium discs and the resultant materials were compared with unmodified titanium coupons. Nanoparticles were physico-chemically analysed to determine their shape, crystallinity, chemical composition, and mean diameter. The materials were incubated for 90 min or 48 h, to evaluate bacterial adhesion or biofilm formation respectively with Staphylococcus aureus or oral mixed bacterial flora composed of Streptococcus oralis, Actinomyces naeslundii, Veionella dispar, and Porphyromonas gingivalis. Ag-NPs help prevent the formation of biofilms both by S. aureus and by mixed oral bacterial flora. Nanoparticles re-irradiated three times showed the biggest antimicrobial effects. Modifying dental implants in this way could prevent the development of peri-implantitis.

Synthesis of gold, platinum, and gold-platinum alloy nanoparticle colloids with high-power megahertz-repetition-rate lasers: the importance of the beam guidance method

Nanoparticles of noble metals and their alloys are of particular interest for biomedicine and catalysis applications. The method of laser ablation of bulk metals in liquids gives facile access to such particles as  high-purity colloids and is already used in industrial research. However, the method still lacks sufficient productivity for industrial implementation into series production. The use of innovative laser technology may help to further disseminate this colloid synthesis method in the near future. Ultrashort-pulsed lasers with high powers and megahertz-repetition-rates became available recently, but place high demands on the accurate optical laser pulse delivery on the target. Full lateral pulse separation is necessary to avoid a reduction of nanoparticle productivity due to pulse shielding. In this study, we compare flexible but rather slow galvanometer scanning with much faster but more expensive polygon-wheel scanning in their performance in the production of colloidal nanoparticles by laser ablation in liquid. Both beam guidance technologies are applied in the laser ablation of gold, platinum, and a gold-rich platinum alloy in micromolar saline water. We found that the dimensions of the scan pattern are crucial. A threshold pattern length exists, at which one scan technology becomes more productive than the other one. In addition, a much lower productivity was found for the ablation of gold compared to that of platinum. Alloying gold with only 10 at.% of platinum improved the productivity nearly to the level of platinum, reaching 8.3 g/h.

Laser-Assisted Synthesis and Oxygen Generation of Nickel Nanoparticles

Nowadays, more than ever, environmental awareness is being taken into account when it comes to the design of novel materials. Herein, the pathway to the creation of a colloid of spherical, almost purely metallic nickel nanoparticles (NPs) through pulsed laser ablation in ethanol is presented. A complex description of the colloid is provided through UV-vis spectroscopy and dynamic light scattering analysis, ensuring insight into laser-induced nanoparticle homogenization and size-control of the NPs. The transmission electron spectroscopy revealed spherical nanoparticles with a narrow size distribution, whereas the energy-dispersive X-ray spectroscopy accompanied by the X-ray photoelectron spectroscopy revealed their metallic nature. Furthermore, an example of the application of the colloidal nanoparticles is presented, where a quick, five-min ultrasound modification results in over an order of magnitude higher current densities in the titania-based electrode for the oxygen evolution reaction.

A simple strategy for enhanced production of nanoparticles by laser ablation in liquids

Upgrading the productivity of nanoparticles (NPs), generated by pulsed laser ablation in liquid (PLAL), still remains challenging. Here a novel variant of PLAL was developed, where a doubled frequency Nd:YAG laser beam (532 nm, ∼5 ns, 10 Hz) at different fluences and for different times was directed into a sealed vessel, toward the interface of the meniscus of ethanol with a tilted bulk metal target. Palladium, copper and silver NPs, synthesized in the performed proof of concept experiments, were mass quantified, by inductively coupled plasma optical emission spectrometry, and characterized by ultraviolet-visible extinction spectroscopy, transmission electron microscopy and x-ray diffraction. The NPs consist of crystalline metals of a few nm size and their ablation rates and agglomeration levels depend on the employed laser fluences. The ensuing laser power-specific productivity curves for each metal, peaked at specific laser fluences, were fitted to the results of a simple model accounting for plasma absorption and heat transfer. The resulting peaked yields and concentrations were more than an order of magnitude higher than those obtained for totally immersed targets. Besides, the measured productivities showed nearly linear dependencies during time intervals up to 30 min of ablation, but became saturated at 1 h, due to accumulation of a significant number of NPs along the laser beam path, reducing the laser intensity reaching the target. The suggested approach that led to enhanced productivities and to generation of high concentrations of NPs in a single vessel could inspire future studies that will contribute to further developments of efficient generation of NPs with controlled characteristics.

Nucleation and growth of gold nanoparticles initiated by nanosecond and femtosecond laser irradiation of aqueous [AuCl4]. Phys Chem Chem Phys 2018;20:28465-28475. [PMID: 30411753 PMCID: PMC6310131 DOI: 10.1039/c8cp05774e]

Irradiation of aqueous [AuCl4]- with 532 nm nanosecond (ns) laser pulses produces monodisperse (PDI = 0.04) 5 nm Au nanoparticles (AuNPs) without any additives or capping agents via a plasmon-enhanced photothermal autocatalytic mechanism. Compared with 800 nm femtosecond (fs) laser pulses, the AuNP growth kinetics under ns laser irradiation follow the same autocatalytic rate law, but with a significantly lower sensitivity to laser pulse energy. The results are explained using a simple model for simulating heat transfer in liquid water and at the interface with AuNPs. While the extent of water superheating with the ns laser is smaller compared to the fs laser, its significantly longer duration can provide sufficient energy to dissociate a small fraction of the [AuCl4]- present, resulting in the formation of AuNPs by coalescence of the resulting Au atoms. Irradiation of initially formed AuNPs at 532 nm results in plasmon-enhanced superheating of water, which greatly accelerates the rate of thermal dissociation of [AuCl4]- and accounts for the observed autocatalytic kinetics. The plasmon-enhanced heating under ns laser irradiation fragments the AuNPs and results in nearly uniform 5 nm particles, while the lack of particles' heating under fs laser irradiation results in the growth of the particles as large as 40 nm.